In a fluid catalytic cracking unit, catalyst flows in a continuous loop from a reactor, to a stripper, to a regenerator and back to the reactor. To maintain the catalyst in a fluidized state, the catalyst must be aerated. For example, a fluidized bed of catalyst is maintained in the regenerator where coke is burned off of the catalyst to regenerate the catalyst before recirculation to the reactor. Air is introduced to the regenerator for both combustion of the coke and fluidization of the catalyst.
In one well-known regenerator design, spent catalyst is conveyed from the stripper to the regenerator through a standpipe and distributed in the regenerator through a spent catalyst distributor. The spent catalyst distributor comprises a vertical centerwell with trough arms extending radially outwardly and downwardly from the top of the centerwell. Spent catalyst is introduced to the bottom of the centerwell where it rises upward through the centerwell and outward through the trough arms to a fluidized bed of catalyst in the regenerator. The spent catalyst flowing through the trough arms is aerated to maintain fluidization and flow. Otherwise, the spent catalyst can flow unevenly through the trough arms and can disrupt operation.
In the prior art design, aeration of the spent catalyst in the trough arms was accomplished by using small-bore piping to convey air to the individual trough arms of the spent catalyst distributor. The regenerator is operated at a high temperature to burn coke off of the catalyst, and the catalyst is abrasive. Consequently, the regenerator is a hostile environment for small-bore piping. Due to this hostile environment, operation of the small-bore piping can be difficult to maintain. Elimination of the small-bore piping used in the regenerator would be desirable to simplify the design of the regenerator and improve the reliability of the unit.